1. Field of the Invention
The present invention relates to the temperature control of electronic components under test, for example, integrated circuits, printed circuits, hybrid circuits and other electronic devices, hereinafter referred to generally as electronic components.
The temperature range over which electronic components have to be tested varies depending on the particular application. For example, in high reliability applications, such as avionics and many civil and military applications it is necessary that electronic components function over the range -55.degree. C. to +125.degree. C. Needless to say, for many other applications there are slightly smaller temperature ranges within which components must function.
2. Description of the Prior Art
The only satisfactory way of testing such components is to provide an environment in which the component can be placed and tested. Any form of localized heating or cooling of a component under test is unsatisfactory. Accordingly, it is necessary to house the component in an enclosure within which the necessary test environment can be created. Generally, such an environment is heated by an electric heater and cooled by some form of gaseous coolant in a two-stage refrigeration system, or by a liquid coolant, for example, evaporation of liquid nitrogen in the enclosure. Unfortunately, two-stage refrigeration systems have to be used because one refrigeration unit alone is incapable of cooling over the temperature range usually required. U.S. Pat. Nos. 4,426,619 and 4,734,872 (Temptronic Corporation) describe a typical system for temperature control of components within a controlled environment in which a gaseous coolant is used. The systems of these inventions include air compressors and dryers, large refrigeration units and an electrical processing unit. Such systems are extremely bulky as a large amount of space is required for the refrigeration and electrical processing units, and for storage containers of cooling gas. As the operation of these systems is complex and much equipment is required, they are extremely expensive both to manufacture and to run. Further, in many such systems the desired accuracy is seldom achieved. Further, these systems are extremely noisy acoustically, and, indeed, a special sound insulating room is sometimes required. Another common problem is the formation of ice on the circuit being tested caused by condensation of atmospheric moisture. Such moisture can produce unwanted electrically conducting paths. Another problem is that components associated with a component under test must generally be located at a relatively large distance from the component under test. This can lead to distortion of test signals. A further problem is that change-over between tests is generally exceedingly time-consuming.